This invention relates generally to improvements in panel fasteners of the type used in aircraft and the like. More specifically, this invention relates to an improved panel fastener particularly for use in aircraft and the like of the so-called stealth type designed to avoid detection by radar.
Panel fasteners are used in large numbers on modern aircraft for removably mounting various panels such as access doors and engine bay covers and the like. Such panel fasteners typically comprise a fastener element such as a bolt having a threaded shank and a head formed to include an appropriate driving slot or recess. A mating driving tool is used for fastener installation to secure the panel prior to normal flight operations, and subsequently as needed for fastener removal to permit appropriate service and/or maintenance functions.
In recent years, substantial research and development efforts have focused upon designing military aircraft capable of avoiding detection by radar. Toward this end, military aircraft have been designed wherein external aircraft surfaces are formed with a geometry and from a material to be substantially nonreflective with respect to standard radar signals. Specifically, such aircraft are constructed to include broad and substantially planar uninterrupted surfaces defined by dielectric material such as composite carbon fiber structures. However, such aircraft necessarily include a number of removable panels such as access doors and engine bay covers to accommodate requisite access to internal mechanisms and electronic equipment, etc. Conventional panel fasteners include fastener heads with recessed driving slots formed therein as previously described, wherein such driving slots present surface interruptions or step discontinuities which can undesirably reflect radar signals and thus permit radar detection of the aircraft.
In the past, panel fasteners for radar avoidance aircraft have required additional structures and/or special treatment steps to avoid undesirable surface discontinuities. In one concept, an auxiliary cap having a dielectric surface coating has been proposed for thread-on attachment to an installed panel fastener. However, the auxiliary cap necessarily requires its own driving slot or recess which still presents a surface discontinuity that can reflect radar signals. In another concept, the head of the panel fastener is covered and filled with a brush-on and curable dielectric material to eliminate surface discontinuities, but such materials must be removed to reveal the fastener driving slot before the fastener can be removed when it is desired to open an access panel.
The present invention overcomes the problems and disadvantages encountered in the prior art by providing an improved panel fastener for use in radar avoidance aircraft and the like, wherein the installed panel fastener substantially eliminates undesired surface discontinuties.